Light Emitting Diode (LED) device and similar semiconductor devices are typically provided with a radiation substrate (a heat sink) for externally radiating heat generated when the device has a semiconductor element driven.
For example, Japanese Patent No. 3862737 (Patent Literature 1) describes that a layer of a first material having high thermal conductivity such as copper (Cu) and a layer of a second material having a small coefficient of thermal expansion such as molybdenum (Mo) and tungsten (W) undergo uni-axial hot pressing (hot pressing) with pressure of not less than 50 kgf/cm2 and not more than 150 kgf/cm2 applied thereto and at a temperature of not lower than 850° C. and not higher than 1000° C. and are thus bonded together to produce a clad material to be used as a radiation substrate for a semiconductor device (see Patent Literature 1, paragraphs [0011], [0015], [0016], [0033], [0034] and the like for example).